The present invention relates to radiation dose calibration instrumentation for use with medical radioisotopes.
Radioisotopes are used in medicine for such purposes as diagnosing a patient's condition, imaging various organs, tumors or malignancies in the body, and providing direct therapeutic treatment of a patient's condition. Typically the radioisotope samples used for such purposes are short-lived, highly radioactive substances that are obtained on demand from a specialized radioisotope generator. The samples are produced by a radioactive decay process occurring within the generator and are prepared for extraction from the generator by various processing steps within the generator. To minimize radiation exposure of the operating personnel, the radioactive decay process and the various processing steps take place within a chamber in the radioisotope generator that is protected by a lead shield. The sample being generated is transferred to a collection vial connected to the generator by a special collection mechanism. The vial is itself usually enclosed in a small, portable shielded container that can be transported easily from the generator to the location where the sample is to be used.
When the collection vial is disconnected from the generator, but before the rapidly decaying radioisotope sample is administered to a patient or otherwise used in a procedure, the vial must be assayed to determine the quantity of contained radioactivity for calibration purposes and for compliance with standards set by the United States Food and Drug Administration the U.S Pharmacopeia, National Formulary &lt;821&gt;. This assay is typically performed in a separate dose calibration apparatus and may expose the operating personnel to harmful radiation. For example, in one common type of dose calibration apparatus known as a re-entry type calibrated gas ionization chamber a worker removes the collection vial from its portable shielded container, transfers the vial to an ionization chamber in the dose calibration apparatus, and, following the assay, transfers the vial back to the portable shielded unit for further processing or dispensing. During this procedure operating personnel are exposed to the radiation emanating from the unshielded collection vial, the exposure being most intense to the fingers, hands and forearms. The exposure to these body parts is usually monitored by a dosimeter placed on a finger, and it is difficult to use the exposure measured in this way to provide accurate estimates of the magnitude and dose distribution to the body parts in question. Notwithstanding the difficulty of measurement, however, the dose to these parts of the body is usually considerably greater than the whole-body dose. Furthermore, this procedure may be repeated often by a single operator for many such samples, and the risk to the practitioner from the cumulative effect may be significant.